Integrating field, microstructural and AMS data to determine the time-relationship between granite emplacement and regional deformation: an example from Calabria (Italy)

Although granites often emplace syntectonically with regional deformation, they are oftenmassive and lack visible foliations.To decipher the internal fabric and kinematics in them,anisotropy of magnetic susceptibility (AMS) is a very useful tool (Mamtani, 2014). In thisstudy, we integrate AMS data with field and microstructural information from the granitoidsof the Serre Batholith (central Calabria), which is tonalitic-granitic in composition (ca. 300Ma in age, Schenk, 1980). The upper crustal metasedimentary rocks of the region arepolydeformed (Angì et al., 2010), and the objectives of the present study are: (a) identify thepresence or absence of deformation textures in the rocks, and (b) work out the timerelationshipbetween emplacement of the batholiths and regional deformation. Most of thegranitoids of the Serre Batholith are unfoliated, and a total of 50 samples were collected forAMS analysis, which was carried out at the IIT Kharagpur (India).Microstructural investigations carried out at the University of Catania (Italy) revealpresence of a variety of deformation textures in the different granitoid rocks. Whilst relictigneous texture such as zoning in feldspars is preserved in some samples, chess-board patternin quartz (high-T solid-state deformation), as well as grain boundary migrationrecrystallization are also developed. Lower-T fabrics such as bulging quartz grain boundaries,deformation twins in feldspar and kinked biotite grains are also common. This implies thatthe Serre granitoids emplaced syntectonically with some regional deformation and developedhigh-T fabrics over which lower-T fabrics were superimposed.AMS data obtained from oriented blocks of the Serre granitoids reveal that some ofthe magnetic foliations tend to be sub-parallel to the S2 foliations of the surrounding rocks,while in general the magnetic fabric is parallel to S3 fabric of the surrounding rocks. Based onthese results, it is inferred that the emplacement of the Serre Batholith initiated during D2regional deformation, and that the granitoid magmas continued to emplace and crystallizewhen the host rocks were being subjected to D3 deformation. Further studies integrating theseresults with the petrogenetic models available for the Serre region are in progress that willenable establishing a comprehensive tectonic history for emplacement and deformation of thegranitoids.